Mr Fairbairn on Fireproof Warehouses. 101 
answers sufficiently for an experiment. The water can be easily 
changed without stopping the action, and it is simpler in its parts. 
Through Mr Crosse’s experiments the sustaining power of the 
water battery is well known. Those in the present communication 
shew the necessity of supplying this battery with water containing 
as much dissolved oxygen as possible. There are many situations 
in the vicinity of surface streams, or of mill-dams, where the requi- 
site water is at command; and it is only there that the value of the 
water battery, for telegraphic or metallurgic purposes, can be fairly 
ascertained. 
I have stated above that strong brine did not at all act on iron 
when the atmosphere was thoroughly excluded. This fact may by 
many be thought sufficient to prove that the salt and water battery 
does not differ from the pure water battery in the principle of its 
action. But as I wished to take as little as possible on trust, I 
repeated all the chief experiments given, substituting sea water, or 
brine, in the place of fresh water. It is unnecessary to go into these 
repetitions, as they all confirm the first results detailed above: and 
the proof has since been rendered still more satisfactory, by placing 
a small zinc and silver couple under the receiver of an air-pump, 
with wires passing through a shell-lac top to connect to the galvan- 
ometer. Such a battery, whether excited by distilled water or by 
sea water, soon loses its action when the air has been well exhaust- 
ed by the air-pump: to do so requires 36 hours. As soon as the 
air is readmitted, a slight deflection of the galvanometer is imme- 
diately observed, but the rise in action is very slow, so long as the 
receiver is kept over the vessel holding the water. When the water 
battery is first subjected to a diminution of pressure, the air rises 
rapidly through the water, which keeps the latter in a state of con- 
tinual motion. This, like shaking by mechanical means, very often 
produces an increase in the action, which, however, is only of a 
temporary nature; for as the water loses its air, the deflection of the 
needles of the galvanometer sinks rapidly. 
The carbonic acid dissolved in water exposed to the atmosphere, 
can have little, or perhaps no effect in these experiments; for when 
water, sparkling with the rapid escape of this gas, is used to excite 
a zinc and silver couple, the action is not quite equal to the result 
produced by rain or sea water. 
On Fireproof Warehouses. By WILLIAM FAIRBAIRN, Esq., 
Civil-Engineer. 
The serious nature of the late fires at Liverpool, Man- 
chester, and other large towns, has induced an inquiry into 
the causes of these disasters, with a view to avert their pro- 
